1. Field of the Invention
The present invention relates to a fisheye attachment to be attached to the object side of a shooting lens of an image-pickup apparatus, such as a still camera or a video camera, to give a fisheye effect. The fisheye attachment according to the present invention is an optical accessory to be detachably attached to a shooting lens to change optical characteristics of the lens.
2. Description of the Related Art
When a fisheye effect, or an effect of giving a distortion that is particularly conspicuous in the peripheral area of an image is desired in photo shooting, an optical accessory such as a converter or an attachment is attached to the object side of a shooting lens in the wide angle end state to produce a large negative distortion as discussed in, for example, Japanese Patent Laid-Open No. H11-305119.
In recent years, with the spread of high definition broadcasting systems represented by the HDTV broadcasting, shooting lenses are required to have high optical performance. Accordingly, high performance optical accessories such as attachments to be attached to such shooting lenses are also demanded. To meet such a demand, it is necessary that aberrations of the optical accessories themselves be corrected satisfactorily.
In particular, fisheye attachments are designed in such a way that a large negative distortion that satisfies the following condition in terms of the image height y, the beam incidence angle θ and the focal length f of the lens is generated.y/(2×f)=sin(θ/2)  (1)
However, the fisheye attachment is generally composed of a single negative lens, which cannot achieve the desired aberration correction. In particular, satisfactory correction of astigmatism and field curvature cannot be achieved.
An object of the present invention is to provide a fisheye attachment having excellent optical performance by correcting aberrations, in particular astigmatism and field curvature.